1. Field of the Invention
The present invention relates to a power conversion device including a protection function with respect to regenerative power from a load.
2. Description of the Background Art
A large number of power conversion devices, typified by inverter devices, are used as drive devices that drive a load such as a motor. This type of power conversion device, in outline, is configured so as to switch an input power supply voltage, which is a rectified commercial power supply, via a semiconductor switching element such as an IGBT (insulated-gate bipolar transistor) or MOSFET (metal-oxide-semiconductor field-effect transistor), thus generating power, for example a three-phase alternating current power, that drives the load (e.g. a motor).
Specifically, a power conversion device 1, as shown in a main portion schematic configuration thereof in FIG. 3, includes a power conversion device main body (inverter device) 2 that switches a direct current power supply voltage Vin, thus generating a three-phase alternating current power that drives a load (motor) M, and a brake circuit 3, provided parallel to the power conversion device main body 2, that protects the power conversion device main body 2 from overvoltage. Reference sign 4 in the drawing is a power supply switch (breaker), reference sign 5 is a rectifier circuit that rectifies an input alternating current voltage Vac, and reference sign 6 is an input capacitor (smoothing capacitor) that smoothes the output voltage of the rectifier circuit 5. The direct current power supply voltage Vin obtained via the input capacitor 6 is supplied to the power conversion device main body 2.
Herein, the brake circuit 3 is installed, for example, between power supply lines of the direct current power supply voltage Vin, and is formed of a series circuit (semiconductor switching circuit) of a resistor 3a and semiconductor switching element (for example, an IGBT) 3b, and a surge voltage absorbing diode 3c connected in parallel to the resistor 3a. The brake circuit 3 forms a current bypass path for the power conversion device main body 2 when the semiconductor switching element 3b is conductive, and performs a role of suppressing (reducing) the direct current power supply voltage Vin applied to the power conversion device main body 2 by causing current to flow through the resistor 3a, thus consuming power.
Also, a control circuit 7 that drives the brake circuit 3 includes, for example, a DC-DC converter 7a, which steps down and detects the direct current power supply voltage Vin, and a comparator 7b that compares the voltage detected by the DC-DC converter 7a and a reference voltage. Further, the control circuit 7 is configured so as to bias a drive circuit 7c when a direct current power supply voltage Vin exceeding a predetermined value (protection voltage) is detected by the comparator 7b, and make conductive and drive the semiconductor switching element 3b of the brake circuit 3 in response to a protection signal output by the drive circuit 7c. 
The function of monitoring the direct current power supply voltage Vin, and protecting the power conversion device main body 2 by driving the brake circuit 3 when the direct current power supply voltage Vin becomes an overvoltage, in this way is as introduced in detail in, for example, JP-A-2005-27424.